were any of the other rod bolts loose when you took them out????
That picture of the main stud length is questionable as to the ability to get proper strech/tension
And I am not reading that you used a strech gage on the rod bolts????? What did you torque them to and what did you use to lube the threads/heads???
Your damage is consistant with a bolt coming out, the cap then breaking the other bolt off---no apparent bearing/
oil problem----